Tumor cell heterogeneity is commonly observed in most hematopoietic and solid tumors which have progressed to the malignant state. The heterogeneity observed is the consequence of substantial differences in gene expression between cells composing such tumors. The mechanisms responsible for heterogeneous gene expression are not well understood. In some lymphoproliferative diseases the heterogeneity appears to be the consequence of cells progressing to different levels of maturation. The proposed research plan utilizes a unique series of cloned cell lines which differ in the kinetics of tumor development, the site of primary organ disease, the expression of numerous surface antigens and mRNA transcripts and the cellular response to glucocorticoid hormones. The applicant has developed and extensively characterized this series of cloned cell lines to address the mechanisms by which lymphoma cells alter their gene expression. From several cell clones which differ in gene expression and tumorigenicity, cDNA libraries were constructed in lambda gt10 and 11. cDNA clones have been isolated by subtraction hybridization screening. These clones represent genes which are expressed in normal thymic lymphocytes but not in liver, brain and other tissues. The proposed research will investigate the mechanism of regulation of these differentially expressed genes and will attempt to identify some of them by DNA sequencing. Cellular differences in sensitivity to glucocorticoid induced lysis will be exploited to isolate hormone responsive genes implicated in the lysis function. The role of differentiation in the occurrence of tumor cell heterogeneity will be further investigated using molecular probes to genes which are sequentially expressed in thymocyte development. The regulation of genes encoding the T-cell antigen receptor, the invariant T3 complex, surface glycoproteins Lyt2 and L3T4, will be examined in detail. By comparing cell clones representing distinct states of maturation and by inducing certain clones to undergo maturational events, the regulation of specific genes will be assessed. Thymic stromal cells have induced some SL12 clones to expressed genes necessary for T-cell maturation. Further studies to determine the stability of the induced alterations in gene expression and to examine their effect of tumorigenicity are proposed.